OnlyOffice is sketchy.

If you are doing presentations I would highly recommend trying none of the above.

I only use markdown or one of the presentation ready things like marp or reveal.js.

So much better and it's just plain text or html.

You can manage presentations in git, find and replace just works, they look miles better and you can even do some neat tricks like having your students connect to a webpage and follow along on their own computers.

PowerPoint was and is a bad idea for presentations.